1. Field of the Invention
The present invention relates generally to an image forming apparatus and a method for driving a light source.
2. Description of the Related Art
Digital printers based on an electrophotographic process have come to be used in the production printing industry in recent years. In the production printing industry, demands for higher image quality and higher reliability of electrophotographic images are increasing. In reproducibility of thin lines and characters, electrophotographic images are required to achieve higher image quality. In particular, enhancing reproducibility of characters of minute sizes corresponding to two or three points and reducing character thickening resulting from an electrophotographic process are desired.
Further, the occurrence of the distortion of the aspect ratio of characters and shapes of minute sizes deriving from the developing process has been found. Therefore, the demands to reduce such distortion of the aspect ratio in the image have increased.
Under these circumstances, some digital printers used in the production printing industry include an image processor configured to perform image processing on input image data, which is high-resolution multibit data of, e.g., 1,200 dpi (dots per inch) or 2,400 dpi, to increase image quality. If data to be handled by the image processor is multibit data of for example, resolution of 2,400 dpi or 4,800 dpi, degree of freedom in image processing is increased. Furthermore, thinning, smoothing, and the like become applicable even to minute characters and lines where a single 1,200-dpi pixel is heavily used.
Some digital printers used in the production printing industry include an optical scanning device, in which an LDA (laser diode array) or a VCSEL (vertical-cavity surface-emitting laser) is employed as a light source that irradiates a surface of a photoconductor drum, thereby implementing a multiple beam system. The optical scanning device configured as such can form an electrostatic latent image at a resolution of 2,400 dpi or 4,800 dpi, which is higher than that of input image data of 1,200 dpi or higher, and therefore can achieve printing quality with high image quality and high speed.
Using such optical scanning devices as those described above configured to perform image processing using high-resolution input image data or to implement a multiple beam system is effective in enhancing reproducibility of minute characters and thin lines of digital printers in the production printing industry.
However, when image processing is performed by the image processor using high-resolution input image data, the amount of data to be transferred to a light-source-modulation-data generator and a light source driver becomes considerably large. This can disadvantageously increase cost caused by adoption of an interface for increasing productivity and data transfer. More specifically, if input image data handled by the image processor is multibit data of, for example, resolution of 2,400 dpi or 4,800 dpi, the amount of data to be transferred downstream to the light-source-modulation-data generator and the light source driver becomes considerably large, which bottlenecks productivity.
Meanwhile, the light-source-modulation-data generator arranged downstream of the image processor to generate data for driving a light source of the optical scanning device is capable of fast processing of data having a higher resolution. However, because image data transferred to the light-source-modulation-data generator has been converted for printing and does not contain image attribute information, it is difficult for the light-source-modulation-data generator to perform all image processing.
Therefore, there is a need for an image forming apparatus and a method for driving a light source capable of increasing image quality of images containing minute characters and line images by performing image processing easily and with high resolution while solving the problem related to data transfer downstream from an image processor.